Hi Bruno.
I agree that you have three perfectly valid reasons for using the mold method, and I'm sure that others will have different ones.
Having done some molding in the past, and always being annoyed that the "best" method for me at the time(polyurethane foam into silicone rubber) was also the most expensive one, has always pushed me to look for alternatives where possible.
The number of times I've found my design solution worked better if I turned it upside down keeps me twisting things round in my head, and just for once I tried "inside out" as an alternative.
About a mile from me is a quarry producing graded flint and sand, so if I get to a trial stage aggregate materials are no problem, and I've already got a local epoxy supplier I've used before.
All I need is a clear run at a project.
Ho hum.
Regards
John
It's like doing jigsaw puzzles in the dark.
Enjoy today's problems, for tomorrow's may be worse.